1. Field of the Invention
The present invention relates to optical communications, and, in particular, to nodes for optical communication networks that support provisioning of optical signals.
2. Description of the Related Art
A typical optical communication network conforming to the Synchronous Optical Network (SONET) standard, comprises a set of nodes interconnected by fiber optical links. When the optical communication network is based on dense wavelength division multiplexing (DWDM), each optical fiber may simultaneously carry a number of different optical signals, where each different optical signal is transmitted at a different wavelength. In general, the different optical signals transmitted over a single optical fiber may have different data rates. For example, some of the optical signals may be OC3 signals having a data rate of 155 megabits/second (Mb/s), while other optical signals may be OC12 signals having a data rate of 622 Mb/s, and still other optical signals may be OC48 signals having a data rate of 2.5 gigabits/second (Gb/s).
In conventional SONET-based optical communication networks, each node is configured with circuitry designed to provision optical signals for communication with other nodes over their corresponding interconnecting optical links. In general, provisioning of optical signals refers to one or more of (1) adding a new optical signal to the communications, (2) deleting an existing (i.e., live) optical signal, (3) increasing the data rate of an existing optical signal (referred to as a xe2x80x9crate-upgradexe2x80x9d), and (4) decreasing the data rate of an existing optical signal (referred to as a xe2x80x9crate-downgradexe2x80x9d). In conventional nodes for SONET-based optical communication networks, different circuit boards are provided for the different optical signal data rates. For example, a particular node may have one or more circuit boards designed to handle only OC3 signals, one or more other circuit boards designed to handle only OC12 signals, and one or more additional circuit boards designed to handle only OC48 signals.
A typical node for a SONET-based DWDM optical communication network that uses, for example, 40 different wavelengths per fiber may be configured with different numbers of OC3, OC12, and OC48 circuit boards that, taken together, are able to provision up to 40 different customer signals for communication over a given optical fiber with another node. In theory, each DWDM wavelength is able to support the highest bandwidth signal (e.g., OC48). In this example, wavelengths that are assigned OC3 or OC12 optical signals are underutilized in terms of their available data bandwidth.
The present invention is directed to circuitry for nodes in optical communication networks, such as SONET-based DWDM optical communication networks, that enables more efficient use of available data bandwidth. In particular, according to certain embodiments of the present invention, a single circuit board for a node is capable of packing a number of different outgoing customer signals (e.g., OC3/OC12-rate signals) into a single outgoing optimum-rate optical signal (e.g., OC48 optical signal) for transmission at a particular wavelength over an optical fiber to another node. The circuit board is also capable of unpacking a number of different incoming customer signals from a single incoming optimum-rate optical signal received from the other node over the same or a different optical fiber. Moreover, those different outgoing and incoming customer signals may have different data rates (e.g., both OC3-rate and OC12-rate signals packed into a single OC48 optical signal).
As an example, in one embodiment of the present invention for a DWDM optical communication network that uses 40 different wavelengths per optical fiber, where each wavelength can support a different OC48 optical signal, each circuit board in each node of the network is capable of (1) packing up to eight different OC3/OC12-rate outgoing customer signals into a single outgoing OC48 optical signal transmitted at one of the 40 DWDM wavelengths and (2) unpacking up to eight different OC3/OC12-rate incoming customer signals from a single incoming OC48 optical signal transmitted at the same DWDM wavelength. Each node can be configured with 40 such circuit boards for each pair of outgoing and incoming optical fibers (or each optical fiber in the case of bi-directional communications on one fiber), with each circuit board handling a different pair of outgoing and incoming composite OC48 optical signals, each one sent on one of the 40 DWDM wavelengths. Such an embodiment is therefore able to support up to 320 different pairs of outgoing and incoming customer signals per pair of optical fibers, as opposed to the prior art limit of only 40 different pairs of customer signals per pair of optical fibers.
In certain embodiments, the present invention relates to the field of optical networking using DWDM or time division multiplexing (TDM) technology and SONET/SDH (Synchronous Digital Hierarchy) mixed-rate muxing and demuxing of OC3/OC12 optical signals to/from an OC48 DWDM optical signal to increase efficiency of use of network capacity. The invention addresses the complexity problem of off-line and in-line provisioning to add/delete/rate-upgrade/rate-downgrade the mixed-rate signals, while reducing service interruptions of live signals. The invention serves the purpose of simplifying the above-mentioned provisioning with an algorithm-based, automatic assignment of the STS3 time slots in OC48 frames to the provisioned mixed-rate signals and by automatic transmission and execution of the port number to STS3 time slot map in both muxing and demuxing nodes.
In the prior art, muxing and demuxing OC3/OC12 optical signals requires manual mapping of the STS3 time slots to the signals. There is no transmission of the map between the muxing and the demuxing nodes. The disadvantage of the prior art is that each addition/deletion/rate-upgrade/rate-downgrade of an OC3/OC12 signal requires retrieval of the existing time slot assignment map and manual re-assignment of the STS3 time slots in both muxing and demuxing nodes. In the case of an OC3-to-OC12 rate-upgrade or addition of a new OC12 signal, the provisioning may require a re-map of existing signals to new STS3 time slots, which may result in failing those signals for a relatively long time due to lack of synchronization between muxing and demuxing nodes. Manual mapping of the STS3 time slots is time consuming and prone to data entry errors. It may be acceptable in applications when signals are provisioned only once in their lifetime. In TDM/DWDM networks, however, the network provider is interested in a frequent re-provisioning of the network-muxed OC3/OC12 signals to satisfy changing needs for bit-rate and changing owners of the signals.
In one embodiment, the present invention is a first node for an optical communication network, the first node having circuitry comprising (a) a first set of one or more receivers configured to generate an incoming customer data signal and a customer clock from each of one or more incoming electrical customer signals; (b) a first clock-and-data-recovery (CDR) circuit configured to generate a first incoming data signal and a first input clock from an incoming electrical signal having a third frame format at a third data rate; (c) a local clock generator configured to generate a local clock; (d) muxing circuitry configured to combine the one or more incoming customer data signals into an outgoing data signal having the third frame format; (e) demuxing circuitry configured to split the first incoming data signal into one or more outgoing customer data signals; (f) a set of one or more transmitters configured to transmit each outgoing customer data signal as an outgoing electrical customer signal; and (g) timing circuitry configured to select a muxing clock for the muxing circuitry and a demuxing clock for the demuxing circuitry from the one or more customer clocks, the first input clock, and the local clock.
The present invention provides easy to execute, fast, data entry and transmission error free, off-line and in-line automatic provisioning of SONET/SDH point-to-point configuration of muxing and demuxing nodes in the TDM, or DWDM networks.